Electronic musical instrument keying system including attack and decay control



Apnl 28, 1970 F. A. CORDRY 3,509,253

ELECTRONIC MUSICAL INSTRUMENT KEYING SYSTEM INCLUDING ATTACK AND DECAY CONTROL Original Filed July 5, 1963 INVENTOR. Rove A. CoRoQy United States Patent 3,509,263 ELECTRONIC MUSICAL INSTRUMENT KEYING SYSTEM INCLUDING ATTACK AND DECAY CONTROL Floyd A. Cordry, Granada Hills, Califi, assrgnor to Warwick Electronics Inc., Chicago, 111., a corporation of Delaware Continuation of application Ser. No. 293,924, July 5, 1963. This application July 7, 1966, Ser. No. 564,518

' Int. Cl. G10h 1/02, 5/10 U.S. Cl. 84-1.13 9 Claims ABSTRACT OF THE DISCLOSURE A keying network is provided for use in an electronic musical instrument, and which is operated by the keyboard of the instrument. The keying network serves selectively to connect the outputs from a plurality of tone generators to a common bus, and includes back-to-back diodes and an isolating resistance combination to prevent leakage. The keying network also includes sustaining circuitry to prevent the abrupt application or withdrawal of the tone signals to the common bus.

This application is a continuation of copending application Ser. No. 293,924 which was filed July 5, 1963 in the name of the present inventor, now abandoned.

This invention relates to the control of an alternatingcurrent circuit by means of a direct-current voltage, and relates specifically to an electronic organ keyer and sustain circuit.

It is musically undesirable to produce a tone at full volume instantly upon the pressing of a playing key. Likewise, it is not desirable to cut 01f a tone instantaneously. In fact, it is desirable in many instances to sustain a tone and have the note trail oif over a second or more of time.

Also, the musician often wishes to choose the time interval that the note does sustain before becoming inaudible. In some musical scores, he may desire to have the notes sustained for a relatively long period of time and trail off gradually. At other times, it may be desirable to have the lingering tone end abruptly or at some intermediate interval of time.

In fact, in actually turning off the tone, it is desirable that there be an almost imperceptible period of time wherein the tone is sustained rather than having an absolute instantaneous cut-01f. Thus, the tone ends abruptly,

. but not with the suddenness that produces a plop or other undesirable sound. This invention may be adapted to produce such a short interval for the purpose of turning oil? a tone, although technically it may be considered a sustain.

Accordingly, it is an object of this invention to provide an improved and simple circuit means interposed between the primary tone generator and the ultimate'output circuit of an organ, which means is adapted to block the passage of musical tone signals or alternatively to pass the signal.

It is a further object of the invention to provide such an improved and simple circuit, termed a keyer, having the ability of producing a time interval of decreasing intensity of the tone after the organist has released the playing key.

It is a further object of the invention to provide such an improved keyer which may be adapted to operate at selectively chosen time intervals for maintaining the tone over a desired period of time.

It is a further object of the invention to provide such an improved keyer which is capable of passing the alternating currents representing the various tones, and which is controlled by a direct-current biasing potential.

A further object of the invention is to provide such an improved direct-current operated keyer, or gate, for musical signals which are efiectively rectangular, and which keyer has exceptionally high attenuation'characteristics to cut off leakage signals, this being achieved by eminently simple diode circuitry, as will be described.

In order to sustain a tone for a period of time after the organist has released the key switch, it is necessary to produce some diminution of the tone envelope rather than merely to break the circuit. Breaking the circuit produces a sudden stoppage of tone, and this is just the opposite to the effect desired for sustain.

This invention employs devices which conduct current more easily in one direction than the other. This is the definition of a diode given in Modern Dictionary of Electronics, published by Howard Sams & Co., First Edition, page 77.

Hence, for simplicity, the balance of this description will refer only to diodes for the purpose of explanation. Moreover, the ensuing reference to diodes in this description, is intended to be exclusive of transistors which require extraneous excitation circuitry, and which produce gain and amplification effects which are not wanted in the circuitry and system of the present invention.

Prior devices have employed diodes and controls to the diodes for the above-mentioned purpose. However, low leakage and low capacitance diodes are quite expensive, and the use of transistors not only represents an expense from a unit standpoint, but such use also represents additional circuit complexity and the requirement for extraneous excitation means. In order to produce a musical instrument within an acceptable price range, the circuit of the present invention uses inexpensive diodes for the control circuit.

Less expensive diodes, however, normally cannot completely close off the passage of current. They are said to leak Whether this is due to direct-current leakage or capacitance. Hence, if a number of such leaking circuits are connected to the output of the organ, there is evidenced a beehive type of noise termed residual created in the output of the organ. Such noise level is not desired.

Accordingly, it is an important object of the present invention to provide an improved diode keyer which is simple and inexpensive in its construction, yet which has exceptionally good attenuation characteristics with respect to leakage currents from the tone generator.

In order to sustain a tone through a typical diode keyer after removal of a steady control potential, it is possible to discharge a capacitor into the keyer. Thus, in an organ environment, after the organ key is de-activated, the capacitor will supply the direct-current bias voltage to the keyer at an amplitude which decreases with time. Since each key requires a capacitor, it then becomes necessary to use a multiple pole switch to vary the decay time constant by connecting various size capacitors into the keyer. That is, to vary the time constant, the size of the capacitor or load resistance across the capacitor must be varied.

Accordingly, it is a further object of this invention to provide an improved diode keyer circuit and system which permits the use of one single-pole switch for varying the decay time constant factors of each key of an organ simultaneously.

In accordance with the above and other objects which will become apparent hereinafter, a preferred form of the present invention is disclosed in the accompanying drawing wherein;

FIGURE 1 is a schematic circuit diagram to illustrate the basic principles of the present invention;

FIGURE 2 is a time versus amplitude graph illustrat- 3 ing the effect upon a generated tone created by the circuitry of FIGURE 1; and

FIGURE 3 is a schematic circuit diagram of a further matrix of diodes in back-to-back relationship.

The circuitry of FIGURE 1 is shown in schematic form because it may be incorporated into any suitable environment, together with refinement components which will be well understood by electronic engineers and particularly those skilled in the electronic musical instrument art.

A tone generator represented by the block 10, is adapted to provide alternating-current signals in the form of a substantially rectangular wave form. For the purpose of this illustration, the base from which the tone generator operates may be considered to be ground potential or zero voltage. From this base, the signal created is a plus voltage signal.

The balance of this description will be based upon the assumption that the signal created from the generator 10 is a plus voltage signal. However, by reversal of the components and provision of suitable balancing potentials, a negative tone generator signal may be employed and will operate substantially in the manner hereinafter described.

Diode 11 is placed in series with the tone generator and is in eifect a valve or gate through which the tone signal must pass. When diode 11 is biased to pass the tone signal, the signal will be permitted to continue beyond the diode 11. Theoretically, with a perfect diode, when the potential on the anode side 13 of diode 11 opposite the tone generator 10 is negative with respect to the tone generator voltage, the signal is prohibited from passing.

That is, regardless of the positive potential on the anode side 13 of diode 11, if the positive potential on the generator side is higher, the signal will not pass. Once the positive potential generated by the tone generator 10 falls below that on the anode side of the diode 11, the diode conducts.

Therefore, as is well known in the art, the diode 11 may be employed as a gate. If a gradually decreasing control voltage is employed at the anode side 13 of the diode 11, then it will serve also as a control to cause a gradually diminishing tone.

According to this invention, the second diode 12 is placed in back-to-back relationship with the diode 11. In this relationship any signal which is permitted to pass the open diode 11, is further attenuated by the open diode 12. As an example, if the diode 11 is non-conducting and therefore ostensibly blocking the passage of any signal from the tone generator 10, there may be as much as ,5 or A of the signal allowed to leak past the diode.

If only one tone generator were involved, this would be no serious handicap. However, a modern electronic organ has a great number of tone generators, and if $6 or A of the signal from each tone generator were permitted to leak through to a common output, the level becomes audible and annoying.

By cascading two such diodes in back-to-back relationship, the amount of leakage passed by one diode is redhced by a similar percentage by the next diode. Thus, in one of the examples given, if A of the signal were to leak past the diode 11, then the diode 12 would allow only M of that amount to pass and thus attenuate to Vlo'ooo the original signal. Such a level is acceptable in the output of the organ even when a great number of such leakages occur. By using back-to-back diodes in the system of the present invention, the aforesaid signal leakage is reduced to acceptable levels with a minimum of circuitry, and this is achieved by relatively inexpensive diodes.

The term back-to-back used herein is intended to suggest the use of two diodes in either anode-to-anode or cathode-to-cathode relationship. In the circuitry shown, the generator is designed to produce a pulse wave form which is positive going. Those skilled in the art 4 will recognize that a tone generator producing a negative pulse wave form may also be employed with proper attention to diode and voltage polarity.

The basic principle on which the present invention is predicated, is the application of a direct-current control voltage to a junction 13 between the diodes 11 and 12. To apply such voltage, a source indicated by the reference character 15 is connected to the junction 13 through a switch 17, resistor 19 and resistor 20, whenever the organ key 21 is pressed to close the switch 17. The purpose in using the two resistors is to minimize signals from other sources working back through the system.

The connection to the output of the organ is on a bus 220 from the junction between resistors 22 and 22A. The value of resistor 22 is high. Signal power from generator 10 is lost because it is high, but amplification at the output restores lost power. The high resistance 22, and the resultant weak signals to bus 22C through similar resistors 22, prevents any appreciable interference energy from returning back through the illustrated system. It will be recognized that resistor 22 and diode 12 may be interchanged without affecting operation of the system.

Upon closing switch 17 to apply voltage to the circuitry thus far described, a condenser 24, groundedat 25, is charged to the extent of the B+ voltage. Therefore, after the switch 17 is opened, the condenser 24 continues to supply voltage to the junction 13 at a decreasing exponential rate and therefore, allowed the signal passing through the diodes 11 and 12 gradually to trail away to an inaudible condition.

The circuitry as thus described will produce a given length of sustain in an exponential decay curve. Some times, however, it is desired to change that curve and cause a faster decay to an inaudible condition. Therefore, a source 26 of B- potential is provided. A switch 27 is connected through a resistor 30 to the junction where condenser 24 connects with the circuit.

Normally, switch 27 will be kept at substantially ground potential by contact with a terminal 31 whenever long sustain is desired. For simplicity, terminal 31 is shown in the drawing at ground potential. Although some of the charge will be drained off to the groundin this manner, there is suificient charge on the capacitor 24 to provide for such loss and yet maintain the circuit for the desired period of time.

In order to shorten the sustained period, switch 27 is moved to make contact with terminal 28. The negative potential of source 26 acts to drain away the charge of' the capacitor 24 at a considerable faster rate than the ground potential of terminal 31, and therefore produce a faster removal of the ground potential from junction 13.

In FIGURE 1 of the drawing, a common bus 32 is employed to connect a multiple number of controls to one switch 27. Thus, rather than attempting to provide a sixty-one fingered switch for a sixty-one note organ, a common bus 32 from all of the systems as illustrated in FIGURE 1 leads to a common switch 27, and thus the source 26 or the ground potential of terminal 31, will operate uniformly on all keys.

In FIGURE 2, there is illustrated a typical graph of tone signal amplitude values versus time. Here it is seen that the envelope surrounding the audible tone is defined by a gradually increasing attack curve 35. The illustration is not intended to be exact, because the attack curve usually is completed in less than one/tenth of one second.

However, the drawing does illustrate the principle involved. This is created by using resistance, such as the resistor 19, to prevent the immediate application of full potential to the junction 13. By allowing the potential to build up slowly, the keyer is put into effect gradually, and thus there is no unpleasant suddenness of sound. Sustain is accomplished by causing the potential at the junction 13 to be removed gradually.

In FIGURE 2, the point 36 represents the time at which the key switch 17 is opened and power supply removed hence, the beginning of the gradual attenuation of the tone. Curve 37 represents the exponential curve of potential delay which results whenever the switch 17 is opened and the charge on capacitor 24 is employed as described. The time interval, as drawn in full lines from the point 36 to an inaudible level, might be one second or more in normal design.

The abscissa of the graph in FIGURE 2 represents zero voltage. Thus, when the signal from the tone generator is pulled down to the zero voltage level, ostensibly there will be no tone passed to the output of the organ.

By using a negative voltage, this tone curve can be reduced faster. The dotted line 38 in FIGURE 2 represents such a condition. As an example, if the B+ voltage from the source is 15 volts, and the B- voltage from the source 26 is 15 volts, then it will be seen that the potential between these two sources is 30 volts. Accordingly,

the dotted line 38 represents the theoretical curve in decay of voltage point 36 down to a negative voltage below the abscissa.

Although the listener does not hear any effect past the position where the line 38 passes the zero potential, or abscissa line, nevertheless the theoretical curve is as illustrated to the full negative position. Thus, the line 38 is caused to decay at a considerable more rapid rate, and this causes the tone to become inaudible at a shortened interval from the time of point 36 to the crossing of the zero potential line, as indicated by the reference number 40.

As an illustration of the means for employing the principles of this invention in a somewhat difierent manner, there is illustrated a collateral circuit employed to produce a substantially instantaneous cut-off of the signal, but actually sustained for a short period of time in order to prevent a sudden clicking sound or disturbing suddenness.

The circuit is shown to comprise a source of potential 41 at a positive voltage substantially equal to the voltage of source 15. A switch 42 connecting through terminal 43 balances the source 41 and the source 15 on opposite sides of a diode 45. Thus, in effect, the diode 45 becomes non-conducting and does not have any effect on the balance of the circuit.

When the switch 17 is opened, the junction between resistors 44 and 19 becomes negative with respect to potential source 41. This condition maintains diode 45 nonconducting.

However, switch 42 has a second terminal 47 connected to a B- voltage indicated by the reference character 48. When the switch 42 is connected to the source 48, there is a potential difierence across the diode 45. This potential causes diode 45 to conduct and drain the charge from condenser 24 at a rapid rate. This, in turn, causes the envelope of FIGURE 2 to drop from the point 36 along the curved line 50.

The curved line 50 is exaggerated in the drawing in order to illustrate the fact of curvature, but is-virtually vertical, illustrating a rapid reduction to zero. Nonetheless, this reduction is not an absolute and instantaneous disconnect, and therefore, the removal of sound is no unpleasant to the ear. Bus 49 is used in the same manner as bus 32 to provide a common control.

As an illustration of the further use of back-to-back diodes, but without sustain characteristics, reference is made to FIGURE 3 of the drawing. In this instance, three leads 60, 61 and 62, including resistance therein, are pro vided from generator sources of varying footages. In the illustration, the small numerals 4, 8 and 16 are placed adjacent the end of the leads 60, 61 and 62, respectively. This is an illustration of one possible combination of footages. Leads 60, 61 and 62 connect through diodes 63, 64 and 65, respectively, to a common junction 70.

A fourth diode 71 is in back-to-back relationship to any one of the three lead diodes, or to all three simultaneously. A control voltage is applied to the junction 70 6 from source 72 through a switch 73 and resistor 74. In this instance, because there is no sustain characteristic when switch 73 is opened, the potential is removed from junction 70 and the back-to-back diodes cause an instantaneous disconnect of tone.

If this were permitted, a clock would occur at the output. Hence, a condenser 75 and resistor 76 are employed. The similarity of the circuit otherwise should be noted, including the ground connection through resistor 22B in order that diode 71 may be activated.

As intimated hereinbefore, the use of a single transistor, instead of the pair of back-to-back diodes 11 and 12, has certain disadvantages which are met by the present invention. In the first place, there are considerable economies efiected by the use of two diodes instead of a single transistor. In todays market, one transistor costs considerably more than two diodes of the characteristics which may be employed in the present invention.

Secondly, the use of a transistor requires the provision of elf-bias voltage to keep the gate non-conductive. In the absence of such an olf-bias voltage, one half-cycle of the tone from the tone generator 10 would pass through the transistor to the output 22. In the present invention, with the simple back-to-back diodes 11 and 12, no such off-bias is required. The two diodes, being positioned backto-back, block both polarities of signal from the tone generator 10.

Furthermore, in the case of a transistor, it is also necessary to provide a collector bias to render the gate operative. No such bias is required in the present invention. Thus, not one but two, bias sources must be provided when a transistor is used, whereas, none whatever is necessary in the present invention.

Thirdly, when the gate is biased to conduction so that signal does pass from the tone generator to the output 22, the tone generator 10 looks into relatively high impedance, represented essentially by the load. In the case of a transistor, however, primarily because of the beta gain of the transistor, the tone generator looks into a very low impendance when the gate is biased to conduction. This produces, in many cases, an objectionably heavy loading on the tone generator 10.

The present invention thus constitutes a recognition that simple, inexpensive, back-to-back diodes, requiring no external operating biases, may be employed in the place of a transistor to effectuate the gating objective of the present circuit.

While the present invention has been shown and described herein in what is conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention which is, therefore, not to be limited to the details disclosed herein, but is to 'be afforded the full scope of the claims.

What is claimed is:

1. In an electronic musical instrument having a keyboard comprising a multiplicity of keys each operable between an actuated and a released position, and further having a common output bus and a plurality of tone generators to be selectively connected to the output bus by the actuation of the aforesaid keys, each of said tone generators producing a pulse signal consisting of a series of discrete pulses extending on one side of a base of reference potential, and further comprising a first resistance means connected to said output bus and to a point of said reference potential; a plurality of keying networks for said tone generators respectively operated by the keys of said keyboard, each of said keying networks including:

first and second unidirectional conductive diode devices each having a cathode terminal and an anode terminal, said diode devices being connected in backto-back relationship with like terminals of said first and second diode devices connected to a common junction, and with the other terminal of said first diode device connected to the output of the corresponding tone generator and the other terminal of said second diode device connected to said common output bus;

a control circuit including capacitance means connected to said common junction and to said point of reference potential, and second resistance means interconnected between said capacitance means and said common junction, a switch coupled to a corresponding key on said keyboard and selectively connecting the junction of said second resistance means and said capacitance means to a first source of unidirectional potential having a potential of a particular polarity with respect to said point of reference potential and of sufiicient value to render said diode devices conductive to the output signal from the corresponding tone generator when said switch is closed, and a discharge circuit for said capacitance means connected thereto.

2. The combination defined in claim 1, in which said control circiut includes a further resistance means in circuit with said switch to prevent the immediate application of full potential from said source to said common junction.

3. The combination defined in claim 2, and which includes isolation resistance means connected in circuit with said second diode device and said output bus to prevent interfering energy from said common bus from entering the keying network.

4. The combination defined in claim 1, and which includes isolation resistance means connected in circuit with said second diode device and said output bus to prevent interfering energy from said common bus from entering the keying network.

5. The combination defined in claim 1, in which said discharge circuit includes further resistance means, and which includes a further switch for selectively connecting said last-named resistance means to said point of reference potential and to a second source of unidirectional potential of opposite polarity to said first source so as to control the discharge time of said capacitance means.

6. The combination defined in claim 1, in which said discharge circuit includes resistance means, and a further switch for selectively connecting said last-named resistance means to a source of unidirectional potential of the same polarity as said first source and to a source of potential of oppoosite polarity to said first source so as to control the discharge time of said capacitance means.

7. The combination defined in claim '6, in which said discharge circuit further includes a diode connectetd in series with said resistance means and said further switch.

'8. The combination defined in claim 1, and which includes a plurality of diodes connecting a corresponding plurality of different tone generators to said common junction.

9. In an electronic musical instrument having a keyboard comprising a multiplicity of keys, each operable between an actuated and a released position, and further having a common output bus, and a plurality of tone generators selectively connectable to the output bus by the actuation of said keys, each of said tone generators produc ing a pulse signal consisting of a train of tone pulses of a given polarity with respect to a reference potential, the combination comprising:

a plurality of pairs of back-to-back diodes forming diode gates, each said diode gate being connected to said output bus;

means connecting said tone generators to said diode gates for pulse driving said diode gates alternately between substantial cutoif and substantially full conduction at the tone frequenecy of the respective tone generator by the train of tone pulses therefrom having said given polarity with respect to a reference potential, so as to produce an output tone signal on said output bus which varies with the magnitude of a sustain bias voltage applied to the diode gate;

each of said diode gates having a biasing circuit comprising resistance means having one terminal connected to the common junction between said back-toback diodes, and a sustain capacitor connected to the other terminal of said resistance means;

key switch means actuated by a respective key and having one terminal connected to the junction between said resistance means and said sustain capacitor; and

a source of potential of said given polarity connected to the other terminal of said key switch means, whereby closing of said key switch means introduces a charge into said sustain capacitor and applies a sustain bias voltage to said gate to cause a pulse signal of tone frequency to appear on said output bus, and whereby opening of said key switch means causes said sustain bias voltage and the magnitude of said output tone signal on said output bus gradually to diminish as the charge on said sustain capacitor gradually diminishes.

References Cited.

UNITED STATES PATENTS 2,618,753 11/1952 Van Mierlo 307-239 X 2,657,318 10/ 1953 Rack 307-243 2,862,171 11/1958 Freeborn 307-317 X 3,047,741 7/ 1962 Snow 307-243 3,143,664 8/1964 Lourie 307-253 3,196,201 7/1965 McDonald 84-1.12 X 3,207,952 9/ 1965 Brahm 84-0 X 3,223,768 12/1965 Munch 84-1.01 3,229,019 1/1966 Peterson 841.24 X 3,297,812 1/1967 Cordry 84-1.01

WARREN F. RAY, Primary Examiner US. Cl. X.R. 

